Memory 2

Activity 1 Research / Revise what cache memory is. 5 minutes

Memory 2 Cache Memory We have already seen cache memory when studying the workings of the CPU. We will now look at it in a little more detail. As we have seen before, RAM will hold a copy of data and instructions (program) that are currently being used by the user. And unfortunately, as the CPU processes data faster than the RAM can supply it with data, system performance can suffer. This is where cache comes in… Learning Objectives: (f) Describe cache memory (g) Describe flash memory (h) Discuss how changes in memory technologies are leading to innovative computer designs.

Memory 2 Cache Memory Cache is simply a few Mb of memory that sits inside the CPU. Being located in the CPU means that data access speed is equal to the CPU’s speed. CPU performance is therefore maintained. Well written programs will make sure that ‘sets’ of regularly used instructions are copied to the cache so that the program can run more efficiently and much faster. Poorly written programs will tend to need to fetch the instructions they need from the RAM one at a time and so as access to the RAM is slow, the program performs less efficiently. Learning Objectives: (f) Describe cache memory (g) Describe flash memory (h) Discuss how changes in memory technologies are leading to innovative computer designs.

Memory 2 How does ‘Cache Memory’ work? Learning Objectives: (f) Describe cache memory (g) Describe flash memory (h) Discuss how changes in memory technologies are leading to innovative computer designs. Efficient programs (algorithms) will enable the CPU to store future instructions to cache so that when the CPU needs them, it can access them super fast

Memory 2 How does RAM store data? Ram holds data using capacitors and transistors. A capacitor can be thought of as a sink or bucket holding water. When it is full it’s holding a ‘bit’ of data (1), when it is empty it represents a zero (0). But obviously in RAM it holds an electrical current (not water). The transistor acts as a switch that lets the computer read the what is in the capacitor (bucket) or fill it up or empty it (change its state). Learning Objectives: (f) Describe cache memory (g) Describe flash memory (h) Discuss how changes in memory technologies are leading to innovative computer designs.

How Capacitors and Transistors Work – a brief overview! Current (electrical flow) Capacitor (holding current) Transistor (switch allowing current to escape) When capacitor is full it represents a ‘ 1 ’ (data) When capacitor is empty it represents a ‘ 0 ’ (data) No Current Flow Current Escapes Capacitor Empties

Memory 2 Types of RAM Dynamic RAM 1 transistor and 1 capacitor for each bit – hold a small charge for a few milliseconds then needs to be refreshed. Because it needs refreshing, there is a limit as to how fast data can be read on this type of RAM. Power always needed. Static RAM 4-5 transistors wired together for each bit of data but it does not lose its charge No need to refresh every few milliseconds – therefore much faster as they don’t need refreshing. Does still need constant electricity supply. Faster but more expensive! Learning Objectives: (f) Describe cache memory (g) Describe flash memory (h) Discuss how changes in memory technologies are leading to innovative computer designs.

Memory 2 Flash Memory (Modern ROM chips and Memory Sticks!) Doesn’t need constant power supply to hold data. They work by sending a large electric current to force electrons through a barrier and trapping them in position. The flash of the electric current used to achieve this gives us the name for this type of memory. The different arrangement of electrons gives us data. Learning Objectives: (f) Describe cache memory (g) Describe flash memory (h) Discuss how changes in memory technologies are leading to innovative computer designs. E E EE EE E E Flash of Electric Current Electrons forced through barrier Arrangement of electrons read by computer

Memory 2 Flash Memory (AKA Solid State) (ROM chips and Memory Sticks!) Main secondary storage device in portable devices. Now-a-days the ROM is flash memory Constant rewriting can cause memory device decline and eventually failure – there are limitations to this type of storage in critical situations devices. Low cost but slower than RAM but is faster than magnetic hard disk so a good option for secondary storage in a PC. Learning Objectives: (f) Describe cache memory (g) Describe flash memory (h) Discuss how changes in memory technologies are leading to innovative computer designs.

Memory 2 The Future? Learning Objectives: (f) Describe cache memory (g) Describe flash memory (h) Discuss how changes in memory technologies are leading to innovative computer designs. TIME DRAM Dynamic SRAM Static ROM Non-Rewritable Non-Volatile Flash Rewritable Non-Volatile Small Storage Large wired transistors/capacitors Big enough to see with eyes Few Kb of data Large Storage Integrated Circuit Millions in the space of a cm 2 Terabytes of data Innovation has driven developments in memory What does the future have to offer?

Activity 2 Complete the ‘How is Data Stored in Computer Memory?’ document 30 minutes